Diverse stressors of chemical and microbial origin can produce lung inflammation and adverse cardio-respiratory health effects. Effects of single agents have been well described clinically and experimentally, however, we hypothesize that chemical and microbial stress can interact to produce a response that is greater than that predicted by the response to single agents alone. Metals, such as nickel (Ni) derived from atmospheric particulate matter (PM) are important components of ambient air pollution associated with adverse health effects. Mycoplasma are a class of microorganism that potentially can produce chronic/persistent/latent infections within the lung with minimal signs of infection. We hypothesize that the presence of microorganisms like mycoplasma will potentiate the inflammatory/immunomodulating potential of chemical stress and, thus, act as co-factors in the genesis or exacerbation of chronic inflammatory and fibrotic lung disease following exposure to PM-derived metals. We will utilize M. fermentans as a prototypic organism capable of latent/subclinical infection or colonization to deliberately infect human lung fibroblasts (HLF) in vitro in order to study the molecular and cellular basis for the synergistic interactions with residual oil fly ash and its attendant metals such as Ni on host-cell production of immune-modulating cytokines such as IL-6. We propose 4 specific aims: 1) To establish and characterize the synergistic interaction of chemical stress (ROFA and Ni exposure) and microbial stress (M. fermentans infection) to stimulate the production of inflammatory and immune-modulating cytokines by HLF 2) To demonstrate that toll-like receptor-2 (TLR-2) specific stimuli (MALP-2) and Ni synergistically interact to produce inflammation and fibrosis within the lung in vivo; 3) To define the importance of Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) in mediating the synergistic interactions between metal-containing Ni and MALP-2; 4) To determine if Ni exposure can enhance activation of innate immunity by microbial components via modulation of the early signaling events of TLR-2 signal transduction. These studies will provide valuable insight into the mechanisms by which microorganisms like M. fermentans upregulate host-defense mechanisms within the lung and modulate the inflammatory response to environmental chemicals. The identification of microbial agents as determinants of host-cell response to chemical stress will necessitate that microbial ecology be taken into consideration in the assessment of risk posed by atmospheric pollutants such as ROFA.